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Cronobacter sp., an opportunistic foodborne pathogen, can cause high mortality in neonatal and premature infants because this pathogen is associated with powdered infant formula (PIF) contamination. Biofilm formation is recognized as the most effective means to help Cronobacter survive throughout the long shelf-life of PIF, thus promoting resistance to cleaning agents and disinfectants. Crystal violet (CV) staining and fluorescence microscopy analyses were used to compare the biofilm formation ability among different Cronobacter strains, and then the weak biofilm former Cronobacter sakazakii ATCC 29544 and the strong biofilm former Cronobacter dubliniensis DSM 18707 were selected for further proteomic analysis. Two-dimensional liquid chromatography–tandem mass spectrometry, which was coupled with isobaric tags for relative and absolute quantification (iTRAQ) labeling, was employed to quantitatively identify the proteins that were differentially expressed in C. sakazakii ATCC 29544 compared to C. dubliniensis DSM 18707. In total, 1190 proteins were detected. Gene Ontology (GO) analysis indicated that these differentially expressed proteins are related to biological binding, cell structure, signal transduction, cell adhesion, and cellular interaction. Among these differential proteins, the expression levels of 177 non-redundant proteins were altered significantly by more than 5-fold, with 96 up-regulated proteins and 81 down-regulated. This study provides important information regarding the cellular requirements for the underlying mechanism of Cronobacter biofilm formation and its survival in harsh environments.

The Oligocene Yacheng Fm contains the most important source rocks that have been confirmed by exploratory wells in the Qiongdongnan Basin. The efficiency of these source rocks is the key to the breakthrough in natural gas exploration in the study area. This paper analyzes the hydrocarbon potential of each sag in this basin from the perspective of control of both source rocks and geothermal heat. Two types of source rocks occur in the Yacheng Fm, namely mudstone of transitional facies and mudstone of neritic facies. Both of them are dominated by a kerogen of type-III, followed by type-II. Their organic matter abundances are controlled by the amount of continental clastic input. The mudstone of transitional facies is commonly higher in organic matter abundance, while that of neritic facies is lower. The coal-measure source rocks of transitional facies were mainly formed in such environments as delta plains, coastal plains and barrier tidal flat-marshes. Due to the control of Cenozoic lithosphere extension and influence of neotectonism, the geothermal gradient, terrestrial heat flow value (HFV) and level of thermal evolution are generally high in deep water. The hot setting not only determines the predominance of gas generation in the deep-water sags, but can promote the shallow-buried source rocks in shallow water into oil window to generate oil. In addition to promoting the hydrocarbon generation of source rocks, the high geothermal and high heat flow value can also speed up the cracking of residual hydrocarbons, thus enhancing hydrocarbon generation efficiency and capacity. According to the theory of joint control of source quality and geothermal heat on hydrocarbon generation, we comprehensively evaluate and rank the exploration potentials of major sags in the Qiongdongnan Basin. These sags are divided into 3 types, of which type-I sags including Yanan, Lingshui, Baodao, Ledong and Huaguang are the highest in hydrocarbon exploration potential.